1. Field of the Invention
The invention relates to a bed water sampling device for simultaneously taking several water samples from the lowest column of water at different heights above the water bed by several cylindrical sample containers which at least one of their front surfaces are provided with a closure actuated by a time-controlled release and which are horizontally oriented for vertical adjustment on a central support rod which terminates in a bottom element and which may be deposited on the water bed by a steel cable attached to its opposite end.
The taking of water samples from the lowest water column, i.e. the bed water above the water bed serves geochemical, oceanographic and (micro-) biological investigations of the transition zone between the water bed (sediment) and the column of water disposed above it. Different exchange processes between these separate sections generate steep gradients of parameters, e.g. in geochemical material concentrations and particle contents which often are very closely intermingled with biological life processes. A bed water sampling device should make high-resolution sampling possible, i.e. sampling at several levels above the bottom of the body of water, the transition zone, in order to allow new insights into the transport and reaction processes prevailing there.
2. The Prior Art
Basically, a distinction has to be made between two types of bed water sampling devices: Arrangements which draw in the water samples from different levels above ground and those in which the water is “caught” by sampling containers arranged at different levels above ground, usually in a horizontal orientation. Among the first mentioned group (taking samples by suction) is, for instance, the water scoop (BIOPROBE) for depths of water up to 600 m in which several sample bottles are vertically arranged on a tripod frame, as mentioned in publication I by L. Thomsen et al.: “An instrument for aggregate studies in the benthic boundary layer” (Marine Geology, 135 (1996), pp. 153-156). Water samples are drawn into the bottles from different levels of the water column by means of suction hoses of different lengths. The disadvantage of this is that while bed water particles may be sampled, their original condition is disturbed by suction of the water samples through the suction hose. Also, the water sample may be subjected to degasification during the suction operation. However, gases dissolved in water often are parameters to be examined. The sample scoop is activated from the water surface, usually from a ship, by a single conductor cable. Since the sampling lasts a relatively long time (30 to 60 minutes), drifting of the ship during the sampling operation may lead to damage of the single conductor cable as a result of twisting. Repairing the single conductor cable by shortening it and renewed placement of the deep sea probe is both very time consuming and expensive. The cable cannot be used for a day otherwise available for taking measurements. Even if the sampler is mounted on a wide-spread tripod frame to minimize current-conditioned eddying and, hence, mixing of the water samples originating from different horizons, its action cannot be avoided altogether. In addition, the suction snorkels themselves constitute flow impediments, so that higher sampling horizons in particular are affected by flow dynamics of any of the more deeply suspended snorkels.
Modifications of the known BIOPROBE water scoop may be gleaned from publication II by L. Thomsen: “Processes in the benthic boundary layer at continental margins and their implication for the benthic carbon cycle” (Journal of Sea Research 41 (1999), pp. 73-86). In BIOPROBE III a hydrodynamically shaped sampler is eccentrically mounted on a mechanically rotatable arm which for the avoidance of mixed sampling is aligned before sample taking in the benthic current by a current sensor. The sampler is vertically arranged and is provided with four sample chambers of 10 I capacity and intake nozzles through which the sample water flows in, at different but rigidly defined levels within a relatively small range of heights (between 5 and 40 cm). However, the principle of nozzles still renders the taking of samples free of particles and without loss of gasses as well as prior rinsing of the sample containers by original bed water problematic. Although current from a battery renders BIOPROBE III self-contained so that it may be used without a single-conductor cable, yet since it is dropped into the water as a free falling apparatus (lander), its recovery operations are time-consuming.
The most closely related state of the art, upon which the present invention is based, is a bed water sampler with an arrangement of horizontally oriented sample containers as described by A. Murdoch et al. in their book “Handbook of Techniques for Aquatic Sediments Sampling”, 2nd edition, pp. 105-106. In this deep sea bed water sampler, several sample bottles structured as cylindrical sample containers, each of 3 I capacity, are mounted and secured against rotation on a central aluminum rod and arranged at different heights changeable over a range of 1.6 m. For its stabilization the central support rod is rigidly mounted on a bottom plate functioning as a bottom element and is supported by three cantilevers. The cantilevers are in turn tensioned by wire cables to a tripod at the upper end of the support rod. This is were a simple wire cable for lowering the sampler is also attached. While it is being lowered, the sampler and, with it, all the sample bottles are not aligned with the current. At one of their end surfaces, the sample bottles are provided with a closure structured as a slidable piston bottom. Their sliding motion is induced pneumatically by a bottle of compressed gas and is controlled by a pressure-protected electronic time release. The sample bottles are to be filled with sample water by way of the piston bottom which results in backup pressure in the interior of the bottle, however, and which may cause disturbance in the taking of the samples such as, for instance, loss of dissolved gasses. Further disturbance during the taking of samples may be caused by the sample bottles not being aligned in the direction of the current so that the sample containers cannot be flushed out by original bed water and by the support cables of the support rod disturbing the current which may lead to mixed samples as a result of eddying.
A bed water sampler with horizontally oriented through-flow sample bottles is known from the joint program of several countries “PROVESS”—Process of Vertical Exchange in Shelf Seas—MAST III (see. PROVESS homepage by Rose Player, Proudman Oceanographic Laboratory, at http://www.pol.ac.uk/provess/html/main.html, last updated on 17 Apr. 2001, State as of 19 Jun. 2002 (see photograph on page http://pol.ac.uk/provess/phographs/b_w_sampler.gif, state 19 Jun. 2002. The photograph reveals ten horizontally oriented transparent sample bottles arranged in superposition on a support scaffold consisting of two parallel support rods centrally fixed in a flaring four-legged frame weighted down by bottom weights. Apparently, the sample bottles are at each end face provided with a closure lid which may be mechanically actuated by a cable mechanism. Hence, for taking samples, the water sample bottles may be freely flushed with water. Further details cannot be discerned from the photograph. Nor does the PROVESS homepage impart further details about the displayed sampler. It can be seen, however, that the sample bottles are rigidly connected to their support frame and that they are surrounded by the four-legged frame. It is, therefore, not possible precisely to align the sample bottles relative to the current for flushing with original bed water and to rinse away sedimentary particles which could have entered the containers while placing the device on the bed. Moreover, the bottom current is dynamically disturbed by the four-legged frame and its cross-braces, so that, again, mixed samples will develop as a result of eddying.